The Justice Department recently questioned military defense attorneys at Guantanamo Bay about whether photographs of CIA personnel, including covert officers, were unlawfully provided to detainees charged with organizing the Sept. 11, 2001, attacks, according to sources familiar with the investigation.

Investigators are looking into allegations that laws protecting classified information were breached when three lawyers showed their clients the photographs, the sources said. The lawyers were apparently attempting to identify CIA officers and contractors involved in the agency’s interrogation of al-Qaeda suspects in facilities outside the United States, where the agency employed harsh techniques.

If detainees at the U.S. military prison in Cuba are tried, either in federal court or by a military commission, defense lawyers are expected to attempt to call CIA personnel to testify.

The photos were taken by researchers hired by the John Adams Project, a joint effort of the American Civil Liberties Union and the National Association of Criminal Defense Lawyers, to support military counsel at Guantanamo Bay, according to the sources, who spoke on the condition of anonymity because of the sensitive nature of the inquiry. It was unclear whether the Justice Department is also examining those organizations.

Both groups have long said that they will zealously investigate the CIA’s interrogation program at “black sites” worldwide as part of the defense of their clients. But government investigators are now looking into whether the defense team went too far by allegedly showing the detainees the photos of CIA officers, in some cases surreptitiously taken outside their homes.

If proved, the allegations would highlight how aggressively both military lawyers and their allies in the human rights community are moving to shed light on the CIA’s interrogation practices and defend their clients. Defense attorneys, however, described the investigation as an attempt by the government to intimidate them into not exposing what happened to their clients.

When contacted about the investigation, the ACLU declined to discuss specifics.

“We are confident that no laws or regulations have been broken as we investigated the circumstances of the torture of our clients and as we have vigorously defended our clients’ interests,” said Anthony D. Romero, the group’s executive director. “Rather than investigate the CIA officials who undertook the torture, they are now investigating the military lawyers who have courageously stepped up to defend these clients in these sham proceedings.”

It is unclear whether the military lawyers under investigation identified the CIA personnel in the photographs to the al-Qaeda suspects or simply asked the detainees whether they had ever seen them. It is also unclear whether the inquiry involves violations of federal statutes prohibiting the identification of covert CIA officers or violations of military commission rules governing the disclosure of classified information, including to the defendants.